1. Field of the Invention
The present invention relates to a novel process for producing 3-methyltetrahydrofuran. More particularly, it pertains to a process for producing, in an efficient and industrially advantageous manner, 3-methyltetrahydrofuran which is useful, for example, as a comonomer for polyether glycol to be used as a starting raw material for spandex fibers, by the use of inexpensive starting raw materials.
2. Description of Related Arts
It is known that 3-methyltetrahydrofuran is a useful compound, for example, as a comonomer for polyether glycol which is a starting raw material for spandex fibers. The 3-methyltetrahydrofuran can be produced by any of a variety of conventional processes, which however, can not necessarily be said to be a satisfactory process because of expensiveness in starting raw materials, low selectivity to the objective product, severe conditions in the reaction or the like.
According to Japanese Patent Application Laid-Open No. 218669/1988, 3-methyltetrahydrofuran is produced together with 3- and 4-methylbutyrolactone by the hydrogenation of citric acid, but the selectivity to the objective product is about 70%. According to U.S. Pat. No. 3956318, 3-methyltetrahydrofuran is produced by the catalytic hydrogenation of an epoxide in liquid phase in the presence of a protonic acid, but the epoxide as a starting raw material is expensive. According to Japanese Patent Application Laid-Open No. 62835/1990, 3-methyltetrahydrofuran is produced by the cyclization of a diol which is obtained by the catalytic hydrogenation of 4-hydroxybutyraldehyde or 2-hydroxytetrahydrofuran in the presence of an aldehyde, but the diol as a starting raw material is expensive and besides, the objective product is accompanied by the by-production of tetrahydrofuran. In addition, there is disclosed a process for producing 3-methyltetrahydrofuran by the hydrogenation of methylmaleic acid or methylsuccinic acid in Japanese Patent Publication No. 9463/1974, but the process is evidently difficult to put into industrial practice, since the starting raw material is difficult to procure and besides the hydrogenation is carried out under severe conditions.
According to Japanese Patent Application Laid-Open No. 22405/1973, 3-methyltetrahydrofuran is produced by a process comprising the steps of hydroformylating 1,4-butenediol in the presence of a catalyst; separating the catalyst from the reactant; then catalytically hydrogenating the aqueous solution of the hydroformylated product which is presumed to be 2-formyl-1,4-butanediol to obtain 2-methyl-1,4-butanediol; and cyclizing the resulting 2-methyl-1,4-butanediol to obtain 3-methyltetrahydrofuran. According to Japanese Patent Laid-Open No. 117258/1993 and Japanese Patent Application Publication No. 55179/1992, 3-methyltetrahydrofuran is produced by the cyclization of diol which is obtained by the catalytic hydrogenation of 1,4-butynediol or 1,4-butenediol in the presence of an aldehyde. However, the 1,4-butynediol and 1,4-butenediol as the starting raw material in the above process are both expensive, since they are obtained from acetylene and besides, the objective product is accompanied with the by-production of tetrahydrofuran.
According to Japanese Patent Application Laid-Open No. 219981/1994, 3-methyltetrahydrofuran is produced together with 2-methyl-1,4-butanediol by the catalytic hydrogenation of itaconic acid, 3-formyl-2-methylpropionic acid or an ester thereof, but the starting raw material composed of itaconic acid or 3-formyl-2-methylpropionic acid is expensive. In view of the above, the conventional processes as mentioned above are far from satisfactory from the industrial point of view because of expensiveness in starting raw material, low selectivity to the objective 3-methyltetrahydrofuran or the like.